Research On Modeling And Control Strategy Of Hybrid AC/DC Microgrid

Under the increasingly severe situation of energy and environmental issues,the advantages of distributed new energy used by connected to microgrids have been widely recognized.With the development of microgrid technology,microgrids have gradually developed into three specific forms: the AC microgrids,the DC microgrids,and the hybrid AC/DC microgrids.Considering the shortcomings of single AC or DC microgrid in terms of system control and economy,this thesis studies the modeling and coordinated control of hybrid AC/DC microgrids that can take into account the advantages of both AC and DC microgrids,and Coordinated control strategies under different operating conditions in different operating modesb are proposed,the system model and its control strategy were verified through simulation.Firstly,based on the summary of the existing research results,the advantages and operating modes of an hybrid AC/DC microgrid system are summarized,and the photovoltaic cells,batteries,various AC/DC power convertersin the hybrid AC/DC microgrid system are modeled and analyzed.Secondly,based on the analysis of system-level control strategy of the microgrid,master-slave control for hybrid AC/DC microgrids is adopted,the AC side storage battery and energy storage converter is set as the main control unit,the DC subsystem and the liaison converter is set as the slave control unit.Subsequently,strategy for photovoltaic cell grid-connected control,battery charge and discharge control,PQ control and V/f control of bidirectional DC/AC converter were designed,simulation analysis were carried out as well.Finally,based on PSCAD/EMTDC simulation software,the power flow of the AC/DC hybrid microgrid system is analyzed in this thesis,the coordinated control strategy under different operating conditions of grid-connected,islanding and islanding/grid-connected switching operation modes are puts forward.and the smooth switching control strategy of islanding V/f control to grid-connected PQ control of the main control unit in the AC/DC hybrid microgrid from island operation to grid switching is designed.By setting up the corresponding AC/DC hybrid microgrid system simulation model,the system simulation analysis was performed from three kinds of different operating modes of the hybrid microgrid.The stability of the AC/DC hybrid microgrid model built in this thesis and the correctness and validity of the proposed coordinated control strategy are proved by the simulation results.